Process for the conversion of sugars to lactic acid and 2-hydroxy-3-butenoic acid or esters thereof comprising a metallo-silicate material and a metal ion

ABSTRACT

A process for the preparation of lactic acid and 2-hydroxy-3-butenoic acid or esters thereof from a sugar in the presence of a metallo-silicate material, a metal ion and a solvent, wherein the metal ion is selected from one or more of the group consisting of potassium ions, sodium ions, lithium ions, rubidium ions and caesium ions.

The present invention relates to a novel process for the preparation oflactic acid and 2-hydroxy-3-butenoic acid or esters thereof from sugarsin the presence of one or more metallo-silicate materials and one ormore metal ions.

BACKGROUND

Carbohydrates represent the largest fraction of biomass and variousstrategies for their efficient use as a feedstock for commercialchemicals are being established. Biomass is of particular interest dueto its potential for supplementing, and ultimately replacing, petroleum.One such commercial chemical obtainable from biomass is lactic acid; alactic acid derivative, methyl lactate, is a convenient building blocktowards renewable and biodegradable solvents and polymers.

Lactic acid derivatives, in particular esters of lactic acid, may beobtained from sugars via a variety of reaction processes includingbiochemical (enzymatic fermentation) and synthetic (catalyticconversion). Particular attention has been focussed on synthetic routesas they provide a commercially and environmentally advantageousalternative to biochemical routes.

EP 2 184 270 B1 and Holm et. al. Science (2010), 328, p 602-605 disclosethe conversion of common sugars to lactic acid derivatives wherein aheterogenous zeotype or zeolite catalyst is employed. Specifically, theconversion of glucose, sucrose or fructose to methyl lactate isdisclosed. A variety of heterogenous Lewis-acid zeotype catalysts areidentified as particularly active catalysts for this conversion. Sn-BEAhas been identified as one of the most selective catalysts, asillustrated by the conversion of glucose, fructose and sucrose to methyllactate with yields of 43, 44 and 68% respectively. There is a desire tofurther improve the percentage yield of useful products such as lactateesters and esters of 2-hydroxy-3-butenoic acid for this process.

In addition to the desire to improve the product yield of such processesusing Sn-BEA as the catalyst, an increase in the product yield usingalternative, easier to synthesize metallo-silicate catalysts wouldbroaden the scope of catalysts suitable for industrially scaledprocesses. A particular advantage would be the application of animproved process and improved catalytic activity wherein the preparationof the catalyst itself is simplified and made suitable for industrialscale production.

Zeotype and zeolite catalysts comprising an active metal can be preparedby several methods including direct synthesis and post-synthesispreparations.

Direct synthesis methods, as described in EP 1 010 667 B1 and ChemCommun. (1997) pp 425-426, although very convenient for laboratory scalesynthesis, may not be suitable for industrial scale production. Thesedirect synthesis procedures experience practical and environmentallimitations posed by: the use of reagents comprising fluoride such ashydrogen fluoride (HF); lengthy synthesis times; and the use ofexpensive organic templating agents which are difficult to reuse.

Recently, Hermans et al Angew. Chem. Int. Ed. (2012), 51, p 11736-11739,disclosed the preparation of Sn-BEA using a post synthesis process thatdoes not require the use of a fluoride reagent. The post synthesisprocess disclosed by Hermans comprises de-aluminating a commerciallyavailable zeolite (Al-BEA), physically mixing this de-aluminated zeolitewith a tin salt, followed by calcination of the de-aluminated zeoliteand tin salt mixture. A general post-synthesis preparation method shouldthus include a step of defect generation in the silica framework viade-alumination or other similar procedure, for example de-boronation;and the addition of tin (Sn) and calcination, which produces theincorporation of Sn in the silica structure.

The post-synthesis preparation process has the advantages of: a shortsynthesis time; the possibility that large amounts of active metal maybe incorporated into the framework structures; and avoidance of the useof expensive organic templating and a reagent comprising fluoride. Theseadvantages enable the process of preparing the Sn-BEA to be scalable andpotentially suitable for industrial scale processes. A similarpost-synthesis methodology has also been applied to the synthesis ofSn-MWW: Qiang et al. ChemSus-Chem [vol 6, issue 8, 1352-1356, August(2013)].

For industrial scale catalyst production, it is a significant advantageif the metallo-silicate catalysts can be prepared by a post synthesisprocess; however, so far reported, all catalysts prepared by the postsynthesis process are poor catalysts for the conversion of C6 sugars tolactate esters and esters of 2-hydroxy-3-butenoic acid. Only low yieldsof the desirable esters are obtained. See Example 1 of the presentapplication.

Therefore there is a desire to improve both the percentage yield of theprocess of preparing lactic acid and 2-hydroxy-3-butenoic acid or estersthereof from sugars, in particular wherein the preparation of thecatalyst is industrially feasible. It would be an additional advantageif the improvement could also broaden the scope of active catalystssuitable for this process and for an industrial scale.

DISCLOSURE OF THE INVENTION

It has now been discovered that the presence of a metal ion, inparticular an alkali earth metal ion and/or an alkali metal ion in thepresence of a metallo-silicate material, can increase the percentageyield of lactic acid and 2-hydroxy-3-butenoic acid or esters thereoffrom sugars. Additionally, this improved process increases the activityof a variety of catalysts for this particular process.

It is particularly surprising that the presence of a metal ion, inparticular an alkali metal ion or alkaline earth metal ion, improves thedesired product yield of this reaction as several literature referencesdisclose the detrimental effect of the presence of an alkali metal ionon the catalytic activity of TS-1 and Ti-BEA catalysts for oxidativecatalytic reactions; or observe no change when added to Sn-BEA underconditions for the isomerisation of glucose to fructose. Bermejo-Devalet al [PNAS, June 19, vol 109, No 25, (2012)] and Khouw et al. J. Catal.151, 77-86, (1995).

Additionally, it can be seen from Examples 13-20 of the presentinvention that specific concentrations of the metal ion provide improvedyields of the desired products. Whilst not wishing the invention to belimited by these results, it can be observed that there may be specificranges of metal ion concentrations that can be seen as an optimisationof the process conditions.

More specifically, the present invention relates to a process for thepreparation of lactic acid and 2-hydroxy-3-butenoic acid or estersthereof from a sugar in the presence of a metallo-silicate material, ametal ion and a solvent, said process comprising contacting the sugar oran isomer or derivative thereof with a metallo-silicate material. Themechanism of the process of the present invention is not fullyunderstood; it may therefore be possible that the process may comprisecontacting the sugar or an isomer or derivative thereof with ametallo-silicate material and the metal ion.

Lactic acid and 2-hydroxy-3-butenoic acid or esters thereof means lacticacid and 2-hydroxy-3-butenoic acid or one or more esters of lactic acid,such as methyl or ethyl lactate, and one more esters of2-hydroxy-3-butenoic acid, such as methyl or ethyl2-hydroxy-3-butenoate.

Sugar relates to carbohydrates commonly found in biomass selected fromone or more of the group consisting of glucose, fructose, mannose,sucrose, xylose, erythrose, erythrulose, threose and glycolaldehyde. Thesugar may be in the form of an isomer of a sugar or a derivative of asugar.

Metal ion relates to a metal ion originating from either the elementitself or the salt of an alkali earth metal and/or an alkali metal. Morespecifically, the salt of the alkaline earth metal or alkali metalcomprises at least one metal ion and at least one anion. Preferably themetal ion is selected from the group consisting of potassium, sodium,lithium, rubidium and caesium. Preferably the salt of the alkaline earthmetal or alkali metal is selected from the group consisting ofcarbonate, nitrate, acetate, lactate, chloride, bromide and hydroxide.Even more preferably the metal ion originates from one or more salts ofthe alkaline earth metal or alkali metal selected from the groupconsisting of K₂CO₃, KNO₃, KCl, potassium acetate (CH₃CO₂K), potassiumlactate (CH₃CH(OH)CO₂K), Na₂CO₃, Li₂CO₃, Rb₂CO₃.

The metal ion may be introduced into the process of the presentinvention either as a component of the metallo-silicate material, orindependently as, for example, a solid or dissolved in a solvent.

Metallo-silicate material (also known as metallo-silicates,metallo-silicate composition or metallo-silicate catalyst) refers to oneor more solid materials comprising silicon oxide and an active metaland/or metal oxide components, wherein the active metal and/or metaloxide components are incorporated into and/or grafted onto the surfaceof the silicon oxide structure (i.e. the silicon oxide structurecomprises M-O—Si bonds). The silicon oxide structure is also known as asilicate. Metallo-silicate materials may display catalytic activity forthe conversion of sugars to derivatives of lactic acid (e.g. esters oflactic acid or esters of 2-hydroxy-3-butenoic acid), lactic acid and2-hydroxy-3-butenoic acid. Metallo-silicate materials may be crystallineor non-crystalline. Non-crystalline metallo-silicate materials includeordered mesoporous amorphous or other mesoporous amorphous forms.Crystalline microporous material includes zeolite materials and zeotypematerials.

Zeolite materials are crystalline alumino-silicates with a microporouscrystalline structure, according to Corma et al., Chem. Rev. 1995, 95 pp559-614. The aluminum atoms of the zeolite material may be partly orfully substituted by an active metal; these materials fall within theclass of zeotype materials. For the purpose of this application zeotypematerials encompass zeolite materials. Preferably the metallo-silicatematerial is selected from one or more of the group consisting of zeotypematerials and ordered mesoporous amorphous silicates.

Active metal relates to the metal that is incorporated into themetallo-silicate material. Active metal means one or more metalsselected from the group consisting of Sn, Ti, Pb, Zr, Ge and Hf.Examples of active metal precursors may be tin chlorides or acetates,for example: SnCl₄; SnCl₂; Sn (IV) acetate; and Sn(II)acetate.

Preferably the active metal is selected from one or more of the groupconsisting of Ge, Sn, Pb, Ti, Zr and Hf. Preferably the zeotype materialhas a framework structure selected from the group consisting of BEA(Beta), MFI, FAU, MOR and FER. Preferably the ordered mesoporousamorphous silicate has a structure selected from the group consisting ofMCM-41 and SBA-15. In a preferred embodiment, the metallo-silicatematerial is selected from the group consisting of Sn-BEA, Sn-MFI,Sn-FAU, Sn-MCM-41 and Sn-SBA-15.

A further aspect of the invention comprises the preparation ofmetallo-silicate materials. Metallo-silicate materials may be preparedby a variety of processes including hydrothermal crystallisation, asdescribed in U.S. Pat. No. 6,306,364 B1; wherein a reaction mixture isprepared by combining reactive sources of tin, silicon an organictemplating agent and water. Alternatively, a zeolite material may bemodified and combined with tin, as described in the post synthesisprocess disclosed by Hermans et. Al., Angew. Chem. Int. Ed. (2012), 51,p 11736-11739. The post synthesis process disclosed by Hermans et al.comprises de-aluminating a commercially available zeolite catalyst(Al-BEA), physically mixing this de-aluminated zeolite catalyst with atin (Sn) salt followed by calcination of the de-aluminated zeolite andtin (Sn) salt mixture.

A further aspect of the present invention is the use of ametallo-silicate material prepared by a post synthesis process. Postsynthesis process means a process comprising preparing a materialcomprising framework defects and impregnating the material with anactive metal or active metal and metal ion. The process for preparing amaterial comprising framework defects is the selective removal of one ormore heteroatoms from a zeolite or zeotype material. The selectiveremoval of one or more heteroatoms from a zeolite or zeotype materialmay be for example de-aluminating or de-boronating a zeolite or zeotypematerial. The material comprising framework defects is impregnated withan active metal, or an active metal and a metal ion.

The process for preparing metallo-silicate materials or metallo-silicatematerials comprising a metal ion may comprise the steps:

-   -   a. Providing one or more zeotype materials or mesoporous        amorphous silicate materials.    -   b. De-aluminating or de-boronating the material of step a.    -   c. Impregnating or mechanically mixing the product of step b.        with an active metal.    -   d. Optionally adding a metal ion to step c.    -   e. Optionally drying the product of step c or d.    -   f. Calcining the product of steps c, d and e.

In a preferred embodiment step b. comprises heating the material of stepa. in acidic conditions or exposing the material of step a. to steam andacidic conditions. In an embodiment of the invention the material ofstep b. is filtered, washed and dried. In an embodiment of the inventionthe material of step b. is filtered, washed and calcined.

In a further preferred embodiment the material of step b. is filtered,washed, dried and calcined.

The heating of step b. may be at a temperature of between about 70 and120° C., between 70° C. and 100° C., between about 70° C. and 90° C.,between 70° C. and 90° C., preferably about 80° C. The heating may occurover a period of time between 2 and 6 hours, between about 11 and 13hours, between 11 and 13 hours.

Acidic conditions as described in the preferred embodiments of step b.may be concentrated acid solutions. Preferably the acid is selected fromthe group consisting of HNO₃, H₂SO₄ and HCl.

All calcination steps are carried out between 400° C. and 600° C.,between 500° C. and 600° C., between 520° C. and 580° C., preferablybetween about 540° C. and about 560° C. Calcination may occur over aperiod of time, for example between about 5 and 7 hours, between 5 and 7hours.

The proper use and understanding of the term impregnation isself-explanatory and lies well within the ability of a person skilled inthe art of catalyst, including metallo-silcate, preparation. Examples ofimpregnation techniques are provided in K. P. de Jong, Synthesis ofSolid Catalysts, Wiley, 2009. ISBN: 978-3-527-32040-0.

A preferred embodiment of the impregnation of step c. is incipientwetness impregnation. A general example of the incipient wetnessimpregnation technique is provided in Campnanati et al. Catalysis Today77 (2003) 299-314. Preferably the impregnation comprises adding anaqueous solution of an active metal precursor to the solid of step b.

A further embodiment of the invention is the preparation of ametallo-silicate material wherein the products of steps d., e. and f.comprise a metal ion. The metal ion is introduced into the product byaddition of a solution of the metal ion during the impregnation step ofstep c.

The present invention provides a process for the preparation ofmetallo-silicate materials and a process for the preparation ofmetallo-silicate materials comprising a metal ion (such as an alkalineearth metal ion or alkali metal ion).

The metallo-silicate materials prepared by post-synthesis treatment ofsilicates with an active metal by incipient wetness impregnation are afurther aspect of the present invention. A preferred embodiment is ametallo-silicate material comprising a metal ion and prepared by a postsynthesis process of the silicate with an active metal.

The metal ion may be introduced into the process of the presentinvention independently of the metallo-silicate material, for example bydissolving the metal ion in the reaction solvent. The metal ion may bedissolved in the reaction solution by adding the metal ion as a metalsalt to the reaction solution or by dissolving the metal salt in asolvent and adding the dissolved metal salt to the reaction solution.

In a further embodiment of the invention, when any metallo-silicatematerial is used in conjunction with K₂CO₃ as metal ion source, theactive metal to metal ion ratio may be between 1 and 20, preferablybetween 2 and 10.

In a further embodiment of the invention, when any Sn-BEAmetallo-silicate material is used in conjunction with K₂CO₃ as metal ionsource, the active metal to metal ion ratio may be between 1 and 20,preferably between 2 and 10. Any Sn-BEA metallo-silicate material meansSn-BEA or Sn-BEA comprising a metal ion.

In a further embodiment of the invention, when catalyst A (Sn-BEA) isused in conjunction with K₂CO₃ as metal ion source, the active metal tometal ion ratio may be between 1 and 20, preferably between 2 and 10,preferably between 3 and 7, more preferably between 3 and 6.

In a further embodiment of the invention, when catalyst A″ (Sn-BEA) isused in conjunction with K₂CO₃ as metal ion source, the active metal tometal ion ratio may be between 1 and 20, between 2 and 16, between 5 and9.5.

In a further embodiment of the invention, when catalyst A is used inconjunction with K₂CO₃ as metal ion source, the initial concentration ofthe metal ion in the solvent is less than 0.5 mmol/L, equal to or lessthan 0.23, between 0.05 mmol/L and 0.25 mmol/L, between 0.06 mmol/L and0.2 mmol/L, between 0.13 mmol/L and 0.17 mmol/L.

The reaction vessel/solution that is used in the process is heated to atemperature of less than 200° C., preferably the vessel is heated tobetween 100° C. and 180° C.; more preferably the vessel is heated tobetween 120° C. and 170° C., even more preferably between 140° C. and160° C.

In a further embodiment of the invention the solvent is selected fromone or more of the group consisting of methanol, ethanol, 1-propanol,1-butanol and water.

In a further embodiment of the invention the percentage yield of lactatefrom sugar is equal to or greater than 50 wt %, equal to or greater than55 wt %, equal to or greater than 60 wt %, equal to or greater than 65wt %, equal to or greater than 70 wt %, equal to or greater than 75 wt%.

In a further embodiment of the invention the percentage yield of methyllactate from sugar is equal to or greater than 50 wt %, equal to orgreater than 55 wt %, equal to or greater than 60 wt %, equal to orgreater than 65 wt %, equal to or greater than 69 wt %, equal to orgreater than 70 wt %, equal to or greater than 75 wt %.

Additionally, the process for the preparation of lactic acid and2-hydroxy-3-butenoic acid or esters thereof of the current invention issuitable for both batch scale reactions and continuous flow reactions.

EXAMPLES

The following examples are provided to illustrate the invention. Theexamples shall not be construed as a limitation of how the invention maybe practised.

Method A: Method for Preparing Methyl Lactate from Sucrose [16 HourReaction Duration].

A stainless steel pressure vessel (40 cc, Swagelok) is charged with amethanol (15.0 g; Sigma-Aldrich, >99.8%) solution of the metal salt(metal ion source), sucrose (0.450 g; Fluka, >99.0%) and catalyst (0.150g). The reactor is closed and heated to 160° C. under stirring (700rpm). The reaction is continued at 160° C. for 16 h and after thisperiod, the reaction is quenched by submerging the vessel in cold water.Samples from the reaction vessel are filtered and analysed by HPLC(Agilent 1200, Biorad Aminex HPX-87H column at 65° C., 0.05 M H₂SO₄, 0.6ml min⁻¹) to quantify unconverted hexoses and dihydroxyacetone (DHA),glyceraldehyde (GLA); and GC (Agilent 7890 with a Phenomenex Solgel-waxcolumn) was used to quantity: methyl lactate (ML), methyl vinylglycolate(MVG, methyl 2-hydroxy-3-butenoate) and glycolaldehyde dimethylacetal(GADMA).

The amount of metal salt is provided for all Examples via the columnentitled: ‘initial metal ion concentration in methanol’.

Method B: Method for Preparing Methyl Lactate from Sucrose [4 HourReaction Duration].

A method for preparing methyl lactate from sucrose as described inMethod A, with the exception that the reaction duration is 4 hours.

Catalyst Preparation: Catalyst A [Sn-BEA (Si/Sn=125)]:

Commercial zeolite Beta (Zeolyst, Si/Al 12.5, ammonium form) is calcined(550° C. for 6 h) to obtain the zeolite Beta H form (de-aluminated form)and treated with 10 grams of concentrated nitric acid (Sigma-Aldrich,65%) per gram of zeolite Beta powder for 12 h at 80° C. The resultingsolid is filtered, washed with ample water and calcined (550° C. for 6h) to obtain the de-aluminated Beta solid.

The de-aluminated Beta solid is impregnated with Sn by incipient wetnessmethodology with a Sn/Si ratio of 125 using the following method: tin(II) chloride (0.128 g, Sigma-Aldrich, 98%) is dissolved in water (5.75mL) and added to the de-aluminated Beta (5 g). After impregnation thesamples are dried 12 h at 110° C. and calcined (550° C. for 6 h).

Catalyst A′ [Sn-BEA (Si/Sn=125) Comprising a Metal Ion]:

Sn-BEA (Si/Sn=125) comprising a metal ion is prepared according to amodification of the previous procedure (preparation of Catalyst A).Commercial zeolite Beta (Zeolyst, Si/Al 12.5, ammonium form) is calcined(550° C. for 6 h) to obtain the H form (de-Aluminated form) and treatedwith 10 g of concentrated nitric acid (Sigma-Aldrich, 65%) per gram ofzeolite Beta powder for 12 h at 80° C. The resulting solid is filtered,washed with ample water and calcined (550° C. for 6 h) to obtain ade-aluminated Beta solid.

The de-aluminated Beta solid is impregnated with Sn and potassium ionsby incipient wetness methodology to obtain a Sn/Si ratio of 125 usingthe following method: tin (II) chloride (0.125 g, Sigma-Aldrich, 98%) isdissolved in a K₂CO₃ solution (5.75 mL of 0.0015 M in water) and addedto the de-aluminated Beta (5 g). After impregnation the samples aredried 12 h at 110° C. and calcined (550° C. for 6 h).

Catalyst A″:

Sn-BEA (Si/Sn=200) is prepared according to a modification of the routedescribed in U.S. Pat. No. 6,306,364 B1. TEOS (30.6 g; Aldrich, 98%) isadded to TEAOH (33.1 g; Sigma-Aldrich, 35% in water) under stirring,forming a two-phase system. After 60-90 min, one phase is obtained.Tin(IV)chloride pentahydrate (0.26 g; SnCl₄.5H₂O, Aldrich, 98%) isdissolved in water (2.0 mL) and added dropwise. The solution is thenleft for several hours under stirring until a viscous gel was formed.The gel is then mineralized by the addition of HF (3.1 g; Fluka, 47-51%)in demineralized water (1.6 g). A suspension of de-aluminated seeds ofSn-BEA (0.36 g) in demineralized water (3.0 g) is added, followed bymanual mixing. The gel is homogenized and transferred to a Teflon-linedcontainer and placed in a stainless steel autoclave and heatedstatically at 140° C. for 14 days. The solid is recovered by filtrationand washed with ample amounts of deionized water, followed by dryingovernight at 80° C. in air. The synthesis is finalized by removing theorganic template by heating the sample at 2° C./min to 550° C. in staticair and maintaining this temperature for 6 h.

Catalyst B [Sn—Y]:

Commercial zeolite Y (Zeolyst, Si/Al 50, hydrogen form) is treated with10 grams of concentrated nitric acid (Sigma-Aldrich, 65%) per gram ofzeolite Beta powder for 12 h at 80° C. The resulting solid is filtered,washed with ample water and calcined (550° C. for 6 h) to obtainde-aluminated Y.

The de-alumintaed Y solid is impregnated with Sn by incipient wetnessmethodology with a Sn/Si ratio of 125 using the following method: tin(II) chloride (0.124 g, Sigma-Aldrich, 98%) is dissolved in water (7.5mL) and added to de-aluminated Y (5 g). After impregnation the samplesare dried for 12 h at 110° C. and calcined (550° C. for 6 h).

Catalyst C [Sn-MCM-41]:

Sn-MCM-41 is prepared according to the method described by Li, L. et al.[Green Chem. 2011, 13, 1175-1181]. In a typical synthesishexadecyltrimethylammonium bromide (13.0 g; CTABr, Sigma >98%) isdissolved in water (38.0 g). Tetramethylammonium silicate (26.4 g; TMAS,Aldrich, 15-20 wt % in water) is added slowly. The mixture is stirredfor 50 min. Tin(IV)chloride pentahydrate (SnCl₄.5H₂O; 0.179 g; Aldrich,98%) and HCl (0.605 g; Sigma-Aldrich, 37 wt %) are dissolved in water(2.1 g) and added slowly to the solution. The resulting mixture isstirred for 1.5 h and TEOS (12.2 g) is added. The mixture is stirred foranother 3 h and transferred to a Teflon lined autoclave and heated to140 C for 15 h. The solid is recovered by filtration and washed withample amounts of deionized water, followed by drying overnight at 80° C.in air. The synthesis was finalized by removing the organic template byheating the sample at 2° C./min to 550° C. in static air and maintainingthis temperature for 6 h.

Examples 1-6

Method A (16 h reaction) was followed using Catalyst A and the metalsalt (metal ion source). Results are provided in Table 1.

TABLE 1 Initial metal ion concentration in Ratio of Percentage TotalMetal salt methanol active Yield of Conversion [Metal ion (mmol/L) metalto methyl of Hexose Ex source] [M+] metal ion lactate Sugars 1 — — — 2776 2 K₂CO₃ 0.13 5 72 96 3 KNO₃ 0.13 5 23 93 4 KCl 0.13 5 28 95 5Potassium 0.13 5 39 95 Acetate 6 Potassium 0.13 5 46 95 lactate

Examples 7-10

Method A (16 h reaction) was followed using Catalyst A and the metalsalt (metal ion source). Results are provided in Table 2.

TABLE 2 Initial metal ion concentration in Ratio of Percentage TotalMetal salt methanol active Yield of Conversion [Metal ion (mmol/L) metalto methyl of Hexose Ex source] [M+] metal ion lactate Sugars 2 K₂CO₃0.13 5 72 96 7 Li₂CO₃ 0.13 5 59 84 8 Na₂CO₃ 0.13 5 72 97 9 Rb₂CO₃ 0.13 567 98 10 CaCO₃ 0.13 5 18 94

Examples 11-17

Method A (16 h reaction) was followed varying the type ofmetallo-silicate material. The metal salt used as a source of metal ionsis K₂CO₃. Results are provided in Table 3.

TABLE 3 Initial metal ion concentration in Ratio of Percentage Totalmethanol active metal Yield of Conversion (mmol/L) to metal methyl ofHexose Ex Catalyst [M+] ion lactate Sugars 1 A — — 27 76 2 A 0.13 5 7296 11 A′ — 7 71 96 12 A″ — — 26 93 13 A″ 0.13 3 58 73 14 B — — 11 67 15B 0.13 5 67 97 16 C — — 20 79 17 C 0.13 3 52 89

Examples 18-23

Method A (16 h reaction) was followed varying the concentration of themetal ion; the metal salt used as a metal ion source is K₂CO₃. CatalystA is used. Results are provided in Table 4.

TABLE 4 Initial metal ion concentration Ratio of Percentage in activeYield of Total methanol metal to methyl Conversion Ex (mmol/L) [M+]metal ion lactate of Hexose Sugars 1 0 — 27 76 18 0.06 10.3 57 97 190.11 6.2 67 98 2 0.13 5.0 72 96 20 0.14 4.2 72 94 21 0.17 3.9 72 96 220.20 3.2 67 88 23 0.23 2.6 62 73

Examples 24-28

Method A (16 h reaction) was followed varying the concentration of themetal ion; the metal salt used as a metal ion source is K₂CO₃. CatalystA″ is used. Results are provided in Table 5.

TABLE 5 Initial metal ion concentration Ratio of Percentage Total inactive Yield of Conversion methanol metal to methyl of Hexose Ex(mmol/L) [M+] metal ion lactate Sugars 12 0 — 26 93 24 0.03 16.0 57 9725 0.045 9.0 67 93 26 0.055 7.0 69 94 27 0.065 6.5 75 93 28 0.1 4.5 5978 13 0.13 3 58 73

Examples 29-33

Method B (4 h reaction) was followed varying the concentration of themetal ion; the metal salt used as a metal ion source is K₂CO₃. CatalystB is used. Results are provided in Table 6.

TABLE 6 Initial metal ion concentration Ratio of Percentage Total inactive Yield of Conversion methanol metal to methyl of Hexose Ex(mmol/L) [M+] metal ion lactate Sugars 14 0 — 11 67 29 0.07 7.7 33 300.10 6.3 45 31 0.13 5.0 56 32 0.17 4.0 44 33 0.20 3.3 45

Key:

[M+]=Metal ion concentration in the reaction solution.[K₂CO₃]=Metal ion concentration; in this Example the metal ion ispotassium originating from K₂CO₃.%=Percentage Yield of methyl lactate

Conversion of Sugar=Total Conversion of Sugar Starting Material.

FIG. 1:

Examples 1, 2 and 18 to 23: Comparison of methyl lactate yield andconversion of sugar with variation of the metal ion concentration.Method A was followed using Catalyst A.

FIG. 2:

Examples 1, 2 and 12 to 17: Comparison of methyl lactate yield preparedvia Method A using catalysts A, A″, B and C; wherein the reaction iscarried out in pure methanol (i.e. without a metal ion), or methanol anda metal ion (i.e. potassium ions). Methyl lactate yield is significantlyincreased by the addition of a metal ion (i.e. potassium ions).

1. A process for the preparation of lactic acid and 2-hydroxy-3-butenoicacid or esters thereof from a sugar in the presence of ametallo-silicate material, a metal ion and a solvent, said processcomprising contacting the sugar with a metallo-silicate material,wherein the metal ion is selected from one or more of the groupconsisting of potassium ions, sodium ions, lithium ions, rubidium ionsand caesium ions.
 2. A process according to claim 1, wherein the metalion is obtainable by the addition to the process of one or morecompounds selected from the group consisting of K₂CO₃, KNO₃, KCl,potassium acetate (CH₃CO₂K), potassium lactate (CH₃CH(OH)CO₂K), Na₂CO₃,Li₂CO₃ and Rb₂CO₃.
 3. A process according to claim 1, wherein themetallo-silicate material framework structure is selected from the groupconsisting of BEA, MFI, FAU, MOR, FER, MCM and SBA.
 4. A processaccording to claim 1, wherein the metallo-silicate material comprises anactive metal selected from one or more of the group consisting of Sn,Ti, Pb, Zr, Ge and Hf.
 5. A process according to claim 1, wherein themetallo-silicate material is selected from the group consisting ofSn-BEA, Sn-MFI, Sn-FAU, Sn-MCM-41 and Sn-SBA-15.
 6. A process accordingto claim 1, wherein the sugar is selected from one or more of the groupconsisting of glucose, fructose, mannose, sucrose, xylose, erythrose,erythrulose, threose and glycolaldehyde.
 7. A process according to claim1, wherein the solvent is selected from one or more of the groupconsisting of methanol, ethanol, 1-propanol, 1-butanol and water.
 8. Aprocess according to claim 1, wherein the ester of lactic acid is methyllactate or ethyl lactate.
 9. A process according to claim 1, wherein theyield of methyl lactate is equal to or greater than 69%.
 10. A processaccording to claim 1, wherein the metallo-silicate material is preparedusing a post synthesis process.
 11. A process according to claim 1,wherein the metallo-silicate material is prepared by impregnating ade-aluminated or de-boronated zeotype material or mesoporous amorphoussilicate material with an active metal.
 12. A process according to claim1, wherein the metallo-silicate material is prepared by impregnating ade-aluminated or de-boronated zeotype material or mesoporous amorphoussilicate material with an active metal and a metal ion.